The present invention relates to a device for transmission between a primary motor shaft and an output shaft, such as a drive shaft for the wheels of self-propelled machines, such as lawn mowers.
It relates more particularly to a device for transmission of the type comprising a casing within which are disposed a reducing mechanism constituted by a driving member, such as an endless screw in engagement with a driven member, such as a toothed wheel, the driven member, mounted freely rotatably on an output shaft, being adapted to be coupled or uncoupled with said shaft by means of a clutch mechanism mounted on said output shaft.
Transmission devices of the mentioned type are well known to those skilled in this art. In such devices, the members of the reducing mechanism are generally made of metal. The same is true for the constituent pieces of the clutch mechanism. The use of metallic members has various drawbacks. Thus, it leads to a transmission device of relatively great weight. Moreover, the constituent pieces of the mechanism are complicated to produce and of relatively high cost. However, because these mechanical pieces are greatly stressed, the manufacturers have naturally until now avoided the use of synthetic material, experiments that have been carried out resulting in breakage and too rapid wear of the pieces, which is incompatible with a long operating life, particularly in the case of application of such a transmission device to lawn mowers.
An object of the present invention is to provide a transmission device whose design permits the use of synthetic materials for certain pieces conventionally made of metal.
To this end, the invention has for its object a transmission device between a primary motor shaft and an output shaft, such as a drive shaft for the wheels of self-propelled machines, such as lawn mowers, of the type comprising at least one casing within which are disposed a reducing mechanism constituted by a guiding member, such as an endless screw in engagement with a driven member, such as a toothed wheel, the driven member, freely mounted for rotation on the output shaft, being adapted to be coupled or uncoupled with said shaft by means of a clutch mechanism mounted on said output shaft, characterized in that the driven member is a toothed tangent wheel, of synthetic material, at least the constituent material of the teeth of the toothed wheel incorporating a mineral or organic load increasing the resistance to wear of said teeth.
The incorporation of loading for the production of the driven member constituted by a toothed tangent wheel permits lessening the wear of the teeth of the toothed wheel and increasing their resistance. It renders compatible the use of a toothed wheel of synthetic material with a driving member of metal or synthetic material.
The invention also has for its object a self-propelled lawn mower of the type comprising a transmission device between a primary motor shaft and an output shaft for driving the wheels of the mower, this transmission device comprising at least one casing within which are disposed a reducing mechanism constituted by a driving member, such as an endless screw in engagement with a driven member, such as a toothed wheel, the driven member, mounted freely rotatably on the output shaft, being adapted to be coupled or uncoupled with said shaft by means of a clutch mechanism mounted on said output shaft, characterized in that the transmission device is of the mentioned type.